Catalytic process for the cracking of hydrocarbon oils containing metallic contaminants



Jan. 5, 1965 N. w. MITCHELL 3,164,542

CATALYTIC PROCESS FOR THE CRACKING OF HYDROCARBON.

OILS CONTAINING METALLIC CONTAMINANTS A TTORN'E y:

SETTLER INSIDE TOWER Jan- 5, 1965 N. w. MITCHELL 3,164,542

CATALYTIC PROCESS FOR THE CRACKING OF HYDROCARBON OILS CONTAINING ME'I.'AI.J..GV CONTAMINANTS Filed oct. a, 1962 2 sheets-sheet 2 i V3,164,542 Patented Jan.l 5, 1965 United States Patent AOliice This invention relates to a catalytic process wherein hydrocarbons are catalytically converted into more valut able products. In one aspect the invention relates to a catalytic cracking operation wherein the cracking steps are conducted at different levels of conversion whereby different heat requirements result. In another aspect the invention relates to an improved method for supplying heat to a catalytic cracking step. In still another aspect the invention relates to means for supplying heat to a catalytic cracker.

It is known to crack hydrocarbon fluids catalytically to increase the quantity and the quality of the gasoline or motor fuel product. In suchroperations a refractory bottoms product is produced in the ,distillation step following the cracking step for which there is little demand and therefore this bottoms product is usually returned to the cracking operation. It is known to solvent extract this heavy bottoms product and the heavy recycle oil so as to remove aromatic hydrocarbons therefrom, which aromatic hydrocarbons are carbon formers and gas formers. The rainate from the solvent extraction step is lthen recycled to the cracking operation. It is also known to employ two or more cracking zones wherein feed stocks containing differing concentrations of contaminating metals are separately cracked. An improved process for operating a plurality of cracking zones in a hydrocarbon conversion process has recently been proposed wherein a relatively refractory, highly parainic, low metal-content hydrocarbon feed stock is supplied to a first catalytic cracking zone operated at high conversion level; a less refractory, metal-containing hydrocarbon feed stock is supplied to a second catalytic cracking zone operated at low conversion; and the heavy cycle oil and the decant oil from the two cracking zones are solvent extracted to provide a raffinate stream which is passed as a portion of the feed stock to the first catalytic cracking zone. The aromatic extract oil from the solvent extraction step is valuable as a carbon black process feed stock. This new method `of operation has greatly increased the catalyst life in the clean oil cracking step which Vis operated at high conversion levels; however, the clean oil `charged to the clean oil unit has not provided arsuicient coke laydown on the catalyst to provide the required amount of heat in the regeneration step to operate the catalytic cracking unit. The hydrocarbon feed is heated in a furnace or other suitable heater to a temperature below thermal cracking temperature and this feed is then brought up to the desired ltemperature in the catalytic cracking zone byheat supplied from the hot, regenerated catalyst. In the regenera, tion step the catalyst is heated by burning the coke `deposited thereon. In the past additional heaty has been supplied to the clean oil unit by adding torch oil to the regenerator of the clean oil unit. Torch oil is a carbon- `forming, substantially metal-free oil used for lighting the burners in furnaces. This procedure is wasteful of valuable equipment and oil.

According to the present invention a minor portion of the highest boiling fraction of the low level conversion catalytic cracking unit (dirty oil unit) recovered as the bottoms product in the fractional distillation of the catalytic cracking step efluent is passed to the clean oil unit (high level conversion unit) so as to provide a coke laydown on the catalyst which will be suflicient to supply the necessary heat to operate the clean oil unit satisfactorily. The bottoms productrfrom the distillation step following the dirty oil unit will contain metal-contaminated catalyst fines and it would be expected that these catalyst nes would contarninate the clean catalyst in the clean catalytic cracking unit; however, I have found that the introduction of this bottoms product to the clean oil unit not only has no deleterious effect on the clean catalyst therein but instead has resulted in lowering the metal content level of the clean oil unit (entrained in the o-gas from the regeneration step). It appears that these nes pass on through the clean oil unit without attaching themselves to the catalyst and there is no resultant build-up of contaminating metals on the catalyst in the clean oil unit. The bottoms material is a coke former having been once-cracked under mild conditions inthe dirty oil unit and when cracked again in the clean oil unit, produces the desired coke laydown on the clean oil catalyst so that sufficient heat is generated in the clean oil regeneration step to accomplish the desired operation of the clean oil catalytic cracking unit. The bottom product, except for the small amount associated with the catalyst fines, is substantially free from metals so that substantially no metals are deposited on the catalyst in the clean oil unit. The bottoms product removed from the dirty oil unit reduces the `amount of coke produced in the dirty oil unit where more coke is normally produced than is needed for supplying the heat to the reactor.

According to the present invention a process is provided for operating two catalytic cracking units, one for clean oil and one for dirty oil, wherein additional coke is provided in the clean oil unit without causing a build-up of metals on the catalyst; wherein no extraneous oils, such as torch oil, are required; and wherein a relatively metalsfree oil produced `in the dirty oil unit is charged to the clean oil unit to provide the additional coke. According to the present invention a process is provided wherein the vheat supplied tothe clean oil unit is increased, the catalyst-to-oil Weight'ratiotisdecreased, and the net yieldrof products is improved. A` portion of the total bottoms product from the fractionator bottoms from the dirty oil `to add the slurry of catalyst lines and fractionator bottoms to the clean oil unit as a convenient means for disposing of this much'of the fractionator bottoms-catalyst fines slurry.

It is an object of `this invention to provide amethod for supplying heat to the clean oil unit in a catalytic cracking `process wherein a clean oil catalytic cracker and a dirty oil catalytic cracker are utilized. Another object of the invention is Ato provide. a substantially metals-free coke- 4forming oil to a clean oil catalytic cracker.

The provision of means to supply heat to a clean oil catalytic cracking apparatus is another object of this invention. Still anotherobject of this invention is to provide a means for utilizing the bottoms product of a dirty oil unit fractionator without the necessity for having to remove therefrom the catalyst nes. Other objects and advantages fof the present invention will be apparent to one skilled in the `art upon studying the disclosure including the detailed description of the invention and the appended drawing.

. FIGURE l is a diagrammatic How plan of one embodiment of the invention; and

FIGURE 2 is a diagrammatic ow plan of a specific, prepared embodiment of the invention.

Referring now to FIGURE 1 of thevdrawing, a hydrocarbon feed stream of about 42,000 barrels per day is fed to a catalytic cracking zone via conduit 11. This feed stream introduced via conduit 12 is made up of about 29,000 barrels per day of gas oil and other distillates so that the metal oxide content of the feed stream is quite small. Recycle streams which can be introduced via conduits 13, 14, 15 and 35a make up the total feed tothe catalytic cracking zione 10 of about 42,000 barrels per day. A heater 16 heats the fresh feed and recycle cycle oils to a temperature slightly under that at which thermal cracking might occu'r prior to admission to the catalytic cracking zone 10. Hot, vregenerated catalyst is addedv to the catalytic cracking zone 10 via conduit 17 and used catalyst is removed via conduit 18 and passed to a regeneration zone (not shown) and is then returned toy the lcatalytic cracking zone 10 at a temperature higher than catalytic cracking temperature so that the mixture of heated oil and regeneratedcatalyst achieves the desired cracking temperature in the cracking zone. The catalyst can be any desired type of cracking catalyst and in the embodiment of the present invention being described the catalyst is a silica-alumina cracking catalyst. Also, 4in the embodiment of the invention presently being described, the catalytic cracking reactors are of the fluidized ow type employing a finelyV divided catalyst, a regenerator also employing the uid solids flow technique, along with fractionating facilities and other facilities make up the system known in the art as an FCC unit. The hydrocarbon effluent from the catalytic cracking zone 10 is passed via conduit 19 to the product fractionator 20 wherein the eiuent products are separated` into fractions having different boiling ranges from whence C4 and lighter materials are removed via conduit 21, a gasoline cut is removed via conduit 22 and light cycle oil is removed via conduit 23 to form these various products of the process. Heavy cycle oil, removed via conduit V24, and decant oil, removed via conduit 25, are passed to a solvent .extraction plant 27. Catalyst which is entrained in the cracking zone eiuent in conduit 19 is accumulated l'in settling zone 28 which is shown as an external settler communicating with product fractionator by means of conduit 29. The accumulated catalyst fines are re- V,moved from settler 28 Vas a slurry in oil and this slurry by means of heater 33. Recycle streams can be added via conduits 34 and 35. Used catalyst which is employed as make-up catalyst for-catalyticcracking zone 30 is introduced via conduit 36and catalyst is removed and passed through a regeneration zone (not shown) via conduit 37 or discarded via conduit 38. The hydrocarbon efuent from catalytic cracking zone 30 is passed via conduit 39 l to a second product fractionation zone 40. C4 and lighter hydrocarbons removed vvia conduit 41, a gasoline fraction removed via conduit 42, and a light vcycle oil removed via conduit 43 are recovered as products of the process. Heavy cycle oil removed via conduit 44 and decant oil removed via conduit 45 are passed through conduit 46 to the solvent extraction zone 27 along with the oil in conduit 26. The aromatic hydrocarbon product which comprises the extract from solvent extraction zone 27 is recovered via conduit 47 for use as feed to a carbon -black producing plant (not shown) or for other desired use. If desired, a portion of the decant oil-.in conduit v 45 can be passed via conduit 45a and conduit 35a to catalytic cracker 10. Similarly, a portion of the heavy recycle oil in conduit 44 can be passed via conduits 44a, 45a and 35a to reactor 10. Also, if desired, all or a part of the decant oil in conduit 45 can be diverted via conduit 48 through the product stream recovered from solvent extraction zone 27 via conduit 47. The product fractionator 40 is illustrated as having the settling zone inside the tower so that decanted oil is removed from the settling zone via conduit 45 and the slurry of catalyst and oil is removed from lthe settling zone via conduit 35. A portion of the slurry of catalyst and oil vcan bek passed via conduit 35 and 35a to catalytic cracker 10. The raffinate removed from solvent extraction zone 27 is passed via conduit 14 as feed to the catalytic cracking zone 10.

A conventional solvent-extraction process is employed utilizing liquid sulfur dioxide as the solvent to extract aromatic compounds from the oil so as to produce a paraiiinic ranate to be returned to the clean oil cracking zone 10. Any suitable solvent can be utilized to extract thel aromatics from the oil.

Al mild catalytic cracking step, i.e., a catalytic cracking step conducted at low conversion level and low temperature isherein defined as a catalytic cracking step operated at a temperature in the range of about 870 to 900 F. and at a conversion level of about 30 to 40 percent conversion. A severe cracking step, i.e., a catalytic cracking step conducted at high temperature and high conversion level, is herein defined as a 4catalytic cracking step operated at atemperature of about 905 to 930 F. and a conversion level of about 50 to 70 percent conversion.

FIGURE 2 illustrates a specific example of the operation of the invention and demonstrates the advantages obtained by opearting the system according to the invention. Referring now to FIGURE 2, operation according to the invention is indicated by the numerals in parentheses which appear as legends on the various streams. It will be noted that operating conditions generally are unchanged; for example, 800 barrels per hour of topped crude are charged to the dirty oil unit and 1200 barrels per hour of raffinate and gas oil fresh feed are charged to the clean oil unit in both instances, and it will also be noted that the temperature and pressure conditions are the same in the reactors and the regenerators when operating according to the prior art and when operating according to the invention. In the prior art operation 40 barrels per hour of catalyst fines slurry in oil are removed from the bottom of fractionation zone 40 and are passed to the reactor 30 of the dirty oil unit and 160 barrels per hour of heavy cycle oil and decant oil are added to the rainate and gas oil charge to the clean oil unit. When operating according to the invention, barrels per hour of catalyst and oil `slurryare withdrawn from the bottom of fractionation zone 40, are mixed with 100 barrels per hour of combined heavy cycle oil and decant oil and this mixture is charged to the clean oil unit at a point downstream from that of contacting the charge to the clean oil unit with the catalyst removed from the generator of the v n clean oil unit. The ow of catalyst from the regenerator ing through the furnace.

to the reactor 10 of the clean oil unit is reduced from 28 tons per minute to 26 tons per minute, the feed of gas oil and raffinate to thev furnace of the clean oil unit is reduced from 1,360l barrels per hour to 1,200 barrels per hour, and the temperature of the stream is raised from to 720 F. when operating according to the invention instead of being raised to 680 F. according to the prior ,art because of the smaller volume of material pass- In the prior art operation, l0 barrels per hour of torch oil were added to the regenerator of the clean oil u nit in order to supply the vheat required to maintain the temperature of 1150 F. in the regenerator whereas when operating according to the inventionv no torch oil is added because the carbon-forming oil stream' supplied to the reactor -1.0via conduit 35 deposits suicient coke on the catalyst to maintain the temperature of 11507 F. in the regenerator of the clean oil unit.

The clean oil, i.e., the rafiinate and gas oil, at a temperature of about 720 F. contacts the clean regenerated catalyst at l150 F. and then after some reaction has occurred as a result of contacting the oil with the catalyst, the coke-forming oil containing some catalyst from the dirty oil unit is added to the reaction mixture and the mixture is passed to the reactor 10 for completion of the reaction. In this manner the reaction of the clean oil is initiated by clean catalyst and the coke-forming oil is added after the initial reaction. The removal of the coke-forming oil from the dirty oil unit is also beneficial to reactor 30 and this is refiected, at least in part, by the increase in gasoline range products recovered in fractionation zone 40 from 235 barrels per hour to 240' barrels per hour. The gasoline boiling range products removed from fractionati-on zone 2t! of the clean oil unit are also increased from 560 barrels per hour to 570 barrels per hour so that the over-all gasoline boiling range production of the system is increased with no increase in fresh feed to either the dirty oil unit or the clean oil unit.

An unexpected advantage in the operation of the above unit according to the process of the invention has been in the reduction of the metal content of the catalyst in the clean oil unit. During the month prior to practice of the invention the metal content of the catalyst of the clean oil unit as NiO plus V205 was 872 parts per million and `the month following the practice of the invention the metal content was reduced to 662 parts per million. The reason for this reduction in metal content of the catalyst is not presently known; however, the metal content of the catalyst in the clean oil unit has run consistently lower when the system is operated according to the process of the invention. Other advantages which have resulted from operating the system according to the process of the invention includes reduction in fuel gas, electrical power and catalyst requirements. The reduction in the amount of catalyst required in the clean oil unit results in lowering the catalyst/oil ratio which generally improves product dlstribution in the clean oil unit.

As hereinbefore stated the amount of coke-forming oil added to the clean oil unit will be that required to provide the coke laydown on the catalyst necessary to achieve the desired temperature in the clean oil unit catalyst regeneration step. The more carbon there is on the catalyst, the higher the temperature will be in the regeneration step. In the system as herein described the amount of carbon-forming oil passed to lthe clean oil unit will usually be in the range of about 40 to 200 barrels per hour.

Variations and modifications are possible Within the scope of the disclosure without departing from the scope and spirit of the invention.

That which is claimed is:

1. In a process for treating hydrocarbon fiuids wherein a gas oil stream having a low metal contaminant content is catalytically cracked in a severe first catalytic cracking zone and a topped crude stream having a high metal contaminant content is catalytically cracked in a mild second catalytic cracking zone and the efiiuent from each cracking zone is fractionally distilled in a distillation zone to produce a metal contaminated catalyst-containing bottoms product, cycle oils and lighter hydrocarbons, the improvement comprising recovering the light cycle oil and lighter hydrocarbons from said first and second cracking zones as products of the process; recovering and passing a minor portion of the bottoms product from said second cracking zone to said first cracking zone; recovering and solvent extracting the heavy cycle oil and remaining bottoms product recovered from said first and second cracking zones; passing the rafiinate from said solvent extraction step as feed to said first cracking zone; adding new catalyst to said first cracking zone; passing used catalyst from said first cracking zone to said second cracking zone; and recovering the aromatic extract from said solvent extraction step as an additional product of the process whereby the metal contaminated catalyst does not adversely affect the new catalyst in said first cracking zone.

2. In a process for treating hydrocarbon fluids wherein a hydrocarbon stream having a low metal contaminant content is-catalytically cracked in a severe first catalytic cracking step utilizing a clean catalyst in a cracking and regeneration cyclic operation and a hydrocarbon stream having a high metal contaminant content is catalytically cracked in a mild second catalytic cracking step utilizing a metal contaminated catalyst in a cracking and regeneration cyclic operation and the efiiuent from each cracking step is fractionally distilled in a distillation step, the improvement comprising passing a sufficient amount of the bottoms product comprising metal contaminated catalyst and oil slurry recovered from distillation of the efiiuent from the second cracking step to the first cracking step to deposit the amount of carbon on the clean catalyst necessary to raise the temperature of the catalyst in the regeneration cycle to that required in the severe cracking cycle without adversely affecting the clean catalyst in said first catalytic cracking step.

3. The process of claim 2 wherein the iirst catalytic cracking step is conducted at a temperature of about 905 to 930 F. and a conversion level in the range of about 50 to 70 percent conversion; and the second catalytic cracking step is conducted at a temperature in the range of about 870 to 900 F. and a conversion level of about 30 to 40 percent conversion.

4. In a hydrocarbon catalytic cracking system comprising a first catalytic cracking reactor containing clean catalyst, a second catalytic reactor contining metal-contaminated catalyst, distillation means for separately distilling the first and second reactor efliuent streams and solvent extraction apparatus for solvent extracting the heavier hydrocarbons removed from the distillation means, the combination therewith of means to pass a portion of the distillation means bottoms product comprising metal-contaminated catalyst and oil slurry of the second reactor etlluent as a portion of the feed to the first reactor.

5. The apparatus of claim 4 including means to measure and control the quantity of distillation means bottoms product comprising metal-contaminated catalyst and oil slurry passed to the feed to the first reactor.

References Cited in the file of this patent UNITED STATES PATENTS 2,356,697 Rial Aug. 22, 1944 2,881,118 Spann et al Apr. 7, 1959 2,941,936 Harper June 21, 1960 

1. IN A PROCESS FOR TREATING HYCROCARBON FLUIDS WHEREIN A GAS OIL STREAM HAVING A LOW METAL COMTAMINANT CONTENT IS CATALYTICALLY CRACKED IN A SEVERE FIRST CATALYTIC CRACKING ZONE AND A TOPPED CRUDE STREAM HAVING A HIGH METAL CONTAMINANT CONTENT IS CATALYTICALLY CRACKED IN A MILD SECOND CATALYTIC CRACKING ZONE AND THE EFFLUENT FROM EACH CRFACKING ZONE IS FRACTIONALLY DISTILLED IN A DISTILLATION ZONE TO PRODUCE A METAL COMTAMINATED CATALYST-CONTAINING BOTTOMS PRODUCT, CYCLE OILS AND LIGHTER HYDROCARBONS, THE IMPROVEMENT COMPRISING RECOVERING THE LIGHT CYCLE OIL AND LIGHTER HYDROCARBONS FROM SAID FIRST AND SECOND CRACKING ZONES AS PRODUCTS OF THE PROCESS; RECOVERING AND PASSING A MINOR PORTION OF THE BOTTOMS PROD- 